1. Technical Field
The present invention is directed to controlling actuation of a vehicle passenger restraint system and is particularly directed to evaluating whether the rate of change of the vehicle deceleration, referred to herein as jerk, is sufficient to warrant actuation of the restraint system.
2. Prior Art
Actuatable passenger restraint systems for vehicles are well known in the art. Such systems are used to sense a crash condition and, in response to such a condition, to actuate an airbag or lock a seat belt or actuate a pretensioner for a seat belt retractor.
The U. Brede et al. U.S. Pat. No. 3,870,894 discloses an actuatable passenger restraint system employing an electrical transducer for providing an electrical signal indicative of a deployment condition, such as vehicle deceleration, for use in actuating such a restraint system. The transducer employed is a piezoelectric transducer operating as an accelerometer and provides an output signal having a value indicative of vehicle deceleration. That signal is integrated and when the integrated signal reaches a predetermined value, a trigger signal is provided for actuating the restraint system.
The M. Held U.S. Pat. No. 3,911,391 is similar to that of Brede et al., but specifically provides that the integration of the output signal of the accelerometer will only commence when the output signal exceeds a minimum threshold level, thereby preventing triggering of the restraint system when the deceleration is such that it can be safely absorbed by passengers in a vehicle.
The above noted patents to Brede et al. and Held have no provision for providing a trigger signal to actuate a restraint system in response to the rate of change of vehicle deceleration, i.e. jerk, exceeding a threshold level.
The Usuie et al. U.S. Pat. No. 3,762,495 discloses an apparatus for actuating a passenger restraint system in a vehicle which relies, in part, for its operation on sensing whether the rate of change of vehicle deceleration, i.e. jerk, exceeds a threshold level. Usui does not require, however, that the vehicle deceleration exceed a minimum threshold level or that the magnitude of the jerk exceed a jerk threshold level within a fixed period of time in order to trigger the passenger restraint system.
It has been determined that all jerks of sufficient magnitude to exceed a jerk threshold level are not timely with respect to the commencement of the crash condition and should not result in actuation of a passenger restraint system. An example of this may be a telephone pole crash at a relatively low speed on the order of 15 miles per hour. During such a crash the passengers may not be severely injured because the g levels imparted to the passengers are relatively low. Specifically, as the vehicle strikes a telephone pole, a U-shaped hole may be created in the vehicle bumper between its headlights, and the shock of the collision is not immediately transferred to the passengers. At a later point in the crash, the pole may encounter the vehicle engine, causing a jerk condition of sufficient magnitude to actuate the restraint system. However, at this later point in the crash, it may not be necessary to actuate the restraint system. Consequently, depending upon the time occurrence of a jerk, it may not be advisable to actuate the restraint system.